1. Field of the Invention
The present invention relates to a radio signal receiving antenna Comprising an electric conductor attached to a sheet of window glass of an automobile or a building.
2. Description of the Prior Art
FIG. 7 of the accompanying drawings schematically shows a known window glass antenna for automobiles as disclosed in Japanese Laid-Open Utility Model Publication No. 1-146614 published on Oct. 9, 1989.
The conventional window glass antenna, generally designated by the reference numeral 101 in FIG. 7, comprises a plurality of loop-shaped receiving antenna patterns 103 attached to a sheet of window glass 102 and spaced inwardly from the outer peripheral edge thereof, and a connector 104 connected to the receiving antenna patterns 103, the connector 104 serving to pick up received radio signals.
The receiving antenna patterns 103 are interrupted by respective gaps 105, 106, 107 defined therein, so that the receiving antenna patterns 103 have different effective lengths, respectively.
The window glass antenna 101 as it is attached to a window glass sheet may not be able to receive desired radio signals with good sensitivity depending on the configurations of the automobile body on which the window glass antenna 101 is mounted.
FIG. 8 of the accompanying drawings illustrates in cross section the window glass antenna 101 that is mounted on an automobile body.
As shown in FIG. 8, the window glass sheet 102 is attached to the automobile body by a window frame 108 having a flange 109. More specifically, the window glass sheet 102 is bonded to the flange 109 through an adhesive gasket 110, and sealed with respect to the window frame 108 by a gasket 111. The frequency vs. sensitivity characteristic of the window glass antenna 101 is not determined by the shape of the receiving antenna patterns 103 only, but is governed by the shape of the receiving antenna patterns 103 and also by the electromagnetic and electrostatic coupling between the antenna patterns 103 and the window frame 108 and the flange 109, which are an electric conductors.
Therefore, in the case where the window glass antenna 101 is mounted on an automobile body, its frequency vs. sensitivity characteristic is affected by an electric conductor of the automobile body, and in the case where the window glass antenna 101 is mounted on a window frame of a building, its frequency vs. sensitivity characteristic is affected by an electric conductor of the window frame or the building.